Apart from high rotational accuracy, an improvement in speed, a reduction in cost, a reduction in noise, etc. are required of the motors mentioned above. One of the factors determining such requisite performances is the bearing supporting the spindle of the motor. Recently, use of a fluid bearing superior in the above requisite performances has been considered, or such a fluid bearing has been actually put into practical use.
This type of fluid bearing is roughly classified into two categories: a dynamic pressure bearing equipped with a dynamic pressure generating portion for generating dynamic pressure in a lubricant in a bearing gap, and a circular bearing equipped with no such dynamic pressure generating portion (bearing whose bearing surface is of a circular configuration).
For example, in a fluid bearing device incorporated into a spindle motor for a disk drive device such as an HDD, both a radial bearing portion radially supporting a shaft member and a thrust bearing portion supporting it in a thrust direction may be formed of dynamic pressure bearings. As a radial bearing portion in a fluid bearing device (dynamic pressure bearing device) of this type, there is known, for example, a radial bearing portion in which a dynamic pressure groove as a dynamic pressure generating portion is formed in one of the inner peripheral surface of a bearing sleeve and the outer peripheral surface of a shaft member opposed thereto, with a radial bearing gap being formed between those two surfaces (see, for example, Patent Document 1).
When the above-mentioned fluid bearing device is incorporated into a motor for a disk drive device such as an HDD, a hub is provided on the shaft member, and an information storage medium such as a magnetic disk is placed or retained on an end surface of this hub (e.g., see, Patent Document 2). To the portion of the disk hub opposed to a stator coil provided on the stationary side of the motor, there is usually fixed a yoke formed of a magnetic material for improving the magnetic force efficiency between the rotor magnet and the stator coil. As a means for fixing a yoke of this type to the disk hub, there is known, for example, a means using an adhesive.    [Patent Document 1] JP 2003-239951 A    [Patent Document 2] JP 2005-45924 A